1. Field of the Invention
The subject application generally relates to a coating composition. More specifically, the subject invention relates to a coating composition having a low volatile organic compound content.
2. Description of the Prior Art
Coating compositions are well known in the art for various applications, especially in the construction industry for decorative and protective uses. Many coating composition used in the construction industry include a latex component and are commonly referred to as “latex-based” paints. The coating compositions including the acrylic latex component are formulated with additional components in order to promote or hinder certain properties. For example, coalescing solvents are typically used as a key component of the coating compositions. The function of coalescing solvents in the coating compositions including the latex component is to aid in the coalescence of latex particles into a cohesive film by partitioning to the latex component. As a result, the coalescing solvents impart film-formation properties to the coating composition as the coating composition cures. More specifically, the coalescing solvents function to reduce a film-forming temperature of the coating composition and enable the coating composition to coalesce at low temperatures. Further, the coalescing solvents function to elasticize the coating composition after curing, thereby imparting integrity and resiliency to the coating composition after curing as measured by wet scrub resistance. Optimized and complete coalescence is also necessary to enable the coating composition to resist blocking after curing, i.e., the ability of the coating composition to resist sticking to another surface after curing and to resist any change in appearance when it is pressed against that surface for a prolonged period of time. Absent the coalescing solvents, certain coating composition(s) would have insufficient coalescence, leading to incomplete film formation at low temperatures and therefore poor film integrity, and wet scrub resistance, each of which is required in order for the coating composition to be suitable for many coating applications.
Conventional coalescing solvents that are used in the coating compositions, such as Texanol®, which is 2,2,2-trimethyl-1,3-pentanediol monoisobutyrate, and Dowanol® DPnB, which is dipropylene glycol N-butyl ether, are categorized as volatile organic compounds (VOCs). It has been speculated that the volatile coalescing solvents may contribute to the depletion of the ozone layer. For this reason, the use and content of VOCs in coating compositions are subject to regulation in the State of California by the SCAQMD, South Coast Air Quality Management District, as well as other agencies around the globe. Due to the concerns surrounding VOCs, the SCAQMD has placed mandates on manufacturers of coating compositions to reduce VOC content in the coating compositions of non-flat coatings from 150 g/l to 50 g/l, effective Jul. 1, 2006 and flat textured from 100 g/l to 50 g/l VOC effective Jul. 1, 2008. As a result of the California regulations, formulators throughout the U.S. are developing low VOC coatings having less than 150 g/l VOC. Furthermore, associated coating industries, such as the adhesive and the ink segments are also developing low VOC formulations. As a result of the increasingly stringent regulation of VOCs in the coating compositions, manufacturers of the coating compositions have embarked on a quest to develop low VOC or VOC-free coating compositions while maintaining the physical properties that are obtained when the volatile coalescing solvents are used.
In addition to the coalescing solvents, freeze/thaw additives are also included in the coating compositions to improve freeze/thaw performance of the coating compositions. Conventional freeze/thaw additives that are used in conjunction with the volatile coalescing solvents include ethylene glycol (EG), diethylene glycol (DEG), and propylene glycol (PG). The conventional freeze/thaw additives, like the volatile coalescing solvents, are also VOCs as determined by the U.S. EPA and add to the total VOC content in the coating compositions. As such, there is also a drive to replace the volatile freeze/thaw additives with low or non-volatile freeze/thaw additives; however, suitable low or non-volatile freeze/thaw additives that are effective when used with the volatile coalescing solvents have yet to be identified.
Among the wide variety of various additives that are known for use in coating compositions, alcohol alkoxylates are one category of additives that have found use in the coating compositions. Alcohol alkoxylates cover a broad spectrum of agents that perform various functions, such as defoaming, wetting, dispersing, and acting as a surfactant. An example of one type of alcohol alkoxylate has the following formula:X(AO)nHwherein X is selected from the group of linear carbon chains, branched carbon chains, aromatic rings, and combinations thereof, AO is an alkyleneoxy group selected from the group of ethyleneoxy groups, 1,2-propyleneoxy groups, 1,2-butyleneoxy groups, and combinations thereof, and n is from to 1 to 75. Such alcohol alkoxylates, when included in the coating compositions, are present for any of the functions as described above, but the coalescing solvents and freeze/thaw additives are also present in the coating composition. In other words, there has been no recognition of specific alcohol alkoxylates as suitable replacements for volatile coalescing solvents in the coating composition.
Alcohol alkoxylates have been suggested for including in coating compositions for the purpose of reducing the content of other components that are characterized as VOCs. For example, U.S. patent application Ser. No. 10/840,917 (the '917 application) to Ruggiero discloses a specific type of alcohol alkoxylate that may be used in a two-component solvent-based paint as a replacement of conventional VOCs that are used in the paint to provide gloss and soft feel to the paint after drying. More specifically, the alcohol alkoxylates are used as surfactants to influence flow characteristics of the paint during application of the paint to a substrate and to aid in leveling of the paint on the substrate as it is applied, which results in the desired gloss and soft feel.
Although enhanced gloss and soft feel are important for certain applications, the specific alcohol alkoxylates disclosed as suitable in the '917 application are not suitable replacements for volatile coalescing solvents. For example, the '917 application lists “POLY-TERGENT” SLF series alcohol alkoxylates as suitable alcohol alkoxylates. Referring to the Examples section below and, specifically, to the Comparative Examples that include Agent L in place of the coalescing solvent, which is an equivalent of POLY-TERGENT SLF-18, those coating compositions have insufficient low temperature coalescence to be a suitable replacement for coalescing solvents in coating compositions. Further, there is no recognition in the '917 patent that certain alcohol alkoxylates may be suitable replacements for volatile coalescing solvents or that the physical properties obtained by using volatile coalescing solvents can also be obtained by using any of the alcohol alkoxylates disclosed therein.
Due to the deficiencies of the prior art, and the strong demand for reducing VOCs in coating compositions without sacrificing physical properties, there is an opportunity to provide a coating composition including an alcohol alkoxylate as a replacement for volatile coalescing solvents in the coating composition such that the VOC content in the coating composition is less than or equal to 150 g/L without sacrificing physical properties of the coating composition.